A Solution for (Not-) CollapsiblePanelExtender Problems

After 4 hours of intensive working on a collapsible panel extender with a "bubble" problem (click collapse: it collapse.. but at the end of animation it return at the original size), we find a solution for this: the bug is the value of property CollapsedSize.
If it's set to 0 or -1, don't work; if it's set to 1 or more, it works.

It happened on a project over ASP.NET 2.0, with Ajax Control Toolkit 1.0.